I have been trying to create a gallery of images in an interactive PDF. I used to be able to do this with an interactive through the object states panel that was on the right-hand workspace area. This feature is not displaying.

Any idea how to make a looping slideshow without the object states panel? Or, where can I go to find the missing panel? (I have already reset the workspace)

You can get to the panel by choosing Window > Interactive > Object States. But it was never designed to work with interactive PDF. It work with Fixed Layout EPUB files and when publishing using Publish Online. (It could be used in SWF or DPS but those are now out-of-date.)